1. Field of the Invention
The present invention relates to the field of internal combustion engines, high performance and conventional manufactured engines in general use, pertaining to poppet valve operating systems, particularly rocker arm systems for valve actuation pivoting on a shaft, the rocker arm being actuated by push rods and a camshaft.
2. Description of Background Information
Internal combustion engines, including high performance engines and conventionally manufactured engines, having poppet valve systems actuated by rocker arms and push rods that operate at high engine speeds or having high dynamic forces within the valve system require specially designed rocker arm systems for stability and for use in high inertia force conditions. For example, a high performance engine speed may peak at approximately 9200 revolutions per minute. This engine speed corresponds to a valve system actuating at 77 cycles per second. These high engine speeds cause very high inertia forces and high amplitude vibration forces to react on rocker arms and valve system components.
Rocker arms manufactured for performance engines generally have a common design basis. The common design consists of a rocker arm beam body having a needle bearing pressed in the beam body. The rocker arm pivots on a shaft that is rigidly fastened by 2 bolts through the shaft located one on each side of the beam to a mounting base attached to the engine cylinder head. Alternatively, the rocker arm beam body and needle bearing assembly are fitted to pivot on a pedestal or central stud mount.
Engines using push rods to actuate valves often have the push rod skewed in an oblique movement direction offset from the plane of rotation of the pivoting rocker arm, opening and closing the valve. This condition results because engine block and cylinder head castings are complicated with structure in the path areas where push rods operate. The resulting skewed push rod path applies a torque to the rocker arm beam that tends to deform the rocker arm beam and the supporting pivot bearing and pivot shaft mounting. FIG. 1. is a rear elevation view of a conventional high performance rocker arm system. Illustrated is the skewed offset push rod 17 and rocker arm 10 arrangements often found in performance engines. The offset push rod force (OPF) is illustrated by arrows at an angle to rocker arm pivot path 22. There are two improvement areas discussed in following paragraphs that the present invention addresses. First: Improvements for a stabilized rocker arm pivot system suitable for use in pushrod actuated systems. Second: Rocker arm beam improvements for reduction of mass and rotational inertia affects and improved beam stiffness.
The first improvement area: A stabilized rocker arm pivot requires different concepts to correct conventional rocker arm deficiencies. Many conventional rocker arms have skewed offset push rods and have a force vector at an angle reacting with the rocker arm. This condition results in rocker arm problems of torsional distortion and increased friction forces. These problems are primarily due to conventional rocker arm beams having a narrow bearing pressed into the beam, which does not provide sufficient resistive reaction to torsional loads. Instability at the rocker arm fulcrum also occurs because bearings commonly are over-stressed by the dynamic angled forces causing severe edge loading of the narrow bearing elements. The bearings then become excessively loose fitting and unstable to the mounting shaft causing unwanted valve train motion, vibration, valve spring surge and increased friction, all adding to performance loss. The torsional deformation of the rocker arm increases stress within the rocker arm body. Indeed, crack failures are common in the beam area near the push rod connection. These described conditions require precautionary and costly rocker arm replacement after a short service time in performance engines. Providing stable rocker arms is a needed improvement provided by the present invention.
The second improvement area: Reducing rocker arm beam mass is practiced by engineers in order to control inertia effects on the valve system. The purpose is to (1) achieve high engine speeds and aggressive valve actuation and lift rates to increase cylinder filling with air and fuel mixtures for applications requiring increased performance and (2) achieve improved engine efficiency by reducing friction and engine component inertia. A mechanism is required to provide stable, low mass rocker arms having high stiffness that can operate at increasingly high loads. Providing stable low mass rocker arms with reduced polar moment of inertia about the beam pivot axis is a significant factor to improve performance levels accomplished by the present invention.